Machines for accurate grinding are usually built on the general lines of either a lathe or a milling machine. In these machines, the grinding wheel takes the place of the cutting tool, and it is so mounted that it can be revolved at high speeds suited to the work.

The grinding lathe holds work between centers, or in special chucks, and the wheel may be fed along the lathe bed as it revolves in light contact with the cylindrical work to be ground. This machine is used for grinding engine valve stems, piston rods, and any similar cylindrical work. Crank shafts of automobile or other small engines are finished from the rough forging in this machine.

The milling machine form of grinder may be either a plain or a universal machine. Work may be placed on its movable table for flat grinding, or the usual lathe center attachments may be used to support work for internal and external cylindrical or other curved-surface grinding. In these machines, the rapidly revolving grinding wheel takes place of the milling cutter. These machines are used for grinding drills, milling cutters, cams, parts of many articles made in quantity such as guns, pistols, tools, and an endless variety of small castings and forgings requiring machine finishing.

The spindle which carries a grinding wheel and the bearings in which it rests are made with the greatest accuracy possible and are fitted to allow no play whatever between spindle and bearing. Grinding may be either wet or dry, but wet grinding is the more accurate as it prevents inaccuracy due to change in temperature of the piece operated on. The machine must be amply protected from water and grit in wet grinding or from dry grit in dry grinding.